How these two players compare in various stats is summarized in the table below. Discussion follows the table.
Robinson was an overwhelming choice to make the Hall in his first year of eligibility while Santo got very little support (normally a player needs 5% to remain on the ballot but somehow Santo returned to the ballot in 1985 after the low vote in 1980, as shown on his Baseball Reference page). And then Santo never got higher than 43.1%.
The predicted 1st year % comes from my model of voting Estimating Hall Of Fame Vote Percentages For The 1980s. Santo was 16.4% below the prediction (20.3 - 3.9 = 16.4). Robinson was 17.4% above the prediction. As much as both of those predictions are off, they both still pretty much predict that Robinson would make it and Santo wouldn't. Since a player needs 75%to get in, Robinson is just about there (according to the model) and very few guys get to the 60% level without eventually making it. For Santo, very few players start out very low and eventually make it. He also got just 13.4% in 1985.
My model is based mainly on how many all-star games and gold gloves a player has gotten, plus MVP awards and milestones like 3000 hits. World Series performance matters, too. Robinson beat Santo in all-star games 18-8 and 15-5 in Gold Gloves. Santo never played in a World Series, while Robinson played in 4. So it is not a surprise that Robinson did so much better in the voting.
The stats WS, BFW and WAR are all composite stats that attempt to value players using all phases of the game. WS is Bill James stat. Robinson beats Santo by 32 here, but that is not alot, actually. James says that a season with 15 WS is an average season. So all that separates the two is a coupld of extra average seasons by Robinson. James says that 20 WS makes an all-star season while 30 is an MVP type season.
Robinson does beat Santo 10-8 in all-star seasons, but it is very close. Then Santo beats him very easily in MVP type seasons and 3 best straight seasons. So he definitely had a higher peak value than Robinson while coming very close to him in career value.
BFW is batting plus fielding wins from Pete Palmer and the data came from Retrosheet. Santo totally outclasses Robinson in both career value and peak value here.
WAR or Wins Above Replacement is from Sean Smith's site and the numbers in parantheses are their respective ranks among position players in career value. Robinson just barely wins the career fight but Santo is way ahead in peak value.
RCAA or runs created above average, which is park adjusted since it is from the Lee Sinins Complete Baseball Encyclopedia. Santo beats Robinson by a wide margin, but Santo's career ended at 34. Robinson played until he was 40. RCAA can be negative so if a player is still active at older ages his career RCAA can go down. But through age 34, to equalize things, Santo is still ahead 253-85. For Robinson to be better, he would have to be ahead in fielding runs by 168. Maybe he was, but that is alot. Then Santo also has a big edge in peak value.
Looking at PAs, we can see that Santo was able to come close to Robinson's career value while having about 2,400 fewer career PAs. It think the sabermetric evidence is in Santo's favor, yet he has gotten much less support. Perhaps my voting model explains the writers's preferences but Santo can still get in by the Veteran's Committee. I hope they look at him again.